Rotary cutters for cutting various materials are well known in the prior art. For example U.S. Pat. No. 2,568,333--Henschker et al discloses a rotary cutter for cutting a moving metal strip. Henschker et al is concerned with the orientation of the cutting blade so as to obtain a square cut. U.S. Pat. No. 3,410,162--Ruggeri discloses a rotary cutter for cutting patches of microfilm from a roll of film. Rotary scissors cutters have also been used in the prior art to cut individual napkins from a parent roll of napkins stock. Typical of such equipment is a napkin folder manufactured by Bretting Company.
Rotary scissors cutters employ two synchronously rotating rolls. Each roll can have mounted in it one or more knife blades. The mounting of the blades in each roll is such that the cutting edges come together with a scissor like cutting action which progresses down the blades across the width of the web being cut. The web to be cut typically wraps one of the rolls which can be referred to as the anvil roll. The cutting edges of the knife blades mounted in the anvil roll usually travel at the same velocity as the web. In order to have the web cut be perpendicular to the direction of travel of the web, the knife blades are mounted in the anvil roll so that their cutting edges are parallel to the roll axis and at a constant radius from the roll axis. The second roll, generally referred to as the fly knife roll, is usually coupled to the anvil roll with anti backlash gearing which also provides for phase adjustment between the two rolls. In order for the cutting edge of a fly knife blade to provide a progressive cutting action with the cutting edge of an anvil blade, the fly knife blade must be mounted in the fly knife roll so that its cutting edge is located at a gradually changing radius down the length of the fly knife roll and it must be appropriately skewed or warped in the circumferential direction to maintain cutting contact with the anvil blade.
It is also well known in the rotary scissor cutter art, that the distance between the center axis of the anvil roll and the center axis of the fly knife roll is less than the sum of the radius of the locus of the cutting edge of a fly knife blade and the radius of the locus of the cutting edge of an anvil blade. Because of this a point on the cutting edge of the fly knife blade intersects the locus of a point on the cutting edge of the anvil blade at two points. The first intersection occurs as the point on the cutting edge of the fly knife blade is traveling so as to have a component directed towards the center of the anvil roll and the second intersection occurs as the point on the fly knife cutting edge is traveling so as to have a component directed away from the center of the anvil roll. Although from a theoretical standpoint a material can be cut by synchronizing the rotation of the fly knife roll with respect to the anvil roll so that the cutting occurs at either the first intersection or the second intersection, it is believed that for practical considerations all prior art rotary cutters or scissors performed the cutting at the first intersection when the fly knife blade is approaching the center of the anvil roll. The reason for this belief is that in order to cut material at the second point of intersection, when the cutting edge of the fly knife blade is traveling away from the center of the anvil roll, the cutting edge of the fly knife blade will have had to push down upon and deflect the uncut material before making the cut at the second point of intesection. If the material being cut is metal as in the Henschker et al reference or microfilm as in the Ruggeri reference, the material will either be deformed or scuffed so as in all likelihood to be useless. It is also believed that those skilled in the art of applying rotary scissors to the cutting of thin flexible materials such as sanitary paper products, did not consider it practical to cut such materials at the second point of intersection when the cut could readily be accomplished at the first point of intersection as the cutting edge of the fly knife blade is traveling toward the center of the anvil roll.